The in-plane susceptibility gradient causes an echo
shift which results in signal loss and ripple artifact in gradient echo
imaging. This become more severe in the gradient echo EPI due to a low gradient
strength applied in the phase-encoding direction during the long echo train. An
approach of using the z-shim in the PE direction was developed. However, this
method has the same disadvantage of increasing the scan time two or three times
as in the through-plane z-shimming. A new approach is to acquire the echo
signals that are shifted outside the regular data acquisition time by acquiring
more echoes outside the regular TDAQ. This will recover the signal loss as well
as remove the ripple artifact without increasing the scan time significantly.